I generally just match powder and shot by volumetric measure. For example: 70 gr. Ffg(by volume)...approx 1 oz shot. Nice "square" load. Great for cotton tail rabbit. And so on. If you prefer, you can go by dram equivalent as well, to determine powder/shot ratio. As you probably already know, 1 dram equals 27.3 grains.
Once I've settled on a load, I simply match the dram equivalent to grains by volume, for both powder and shot. For example: 3 drams equals about 82 grains(81.9). So, I set my adjustable powder measure for 80 grains.... and use that to measure both powder charge and shot. Close enough for practical purposes.
As for shot size... depends on the game, but normally either 6's or 7 1/2's work very well on small game like rabbit, grouse, etc. Sometimes #8. Number 7 1/2 shot being preferred over all.
Since I don't know what powder charge you currently use for ball, I can't recommend using it as a reference. But, you don't need a heavy powder charge in most hunting situations.
In fact, I rarely go over 80gr Ffg/1 1/8 oz shot(both by volume), for the majority of small game hunting scenarios. I've really never seen the need to go heavier.
With the possible exception of wild turkey. In this case, I normally shoot 90gr. Ffg/ 1 1/4 oz of either #4 or #5 shot(# 5 preferred). Though I will also go to #6, on occasion. As a matter of interest, I took a nice, 22 lb bird with a 1 1/8oz, #6 shot payload, driven by 80 grains Ffg, by volume. Nice combination for in close.....in this case, about 15 yards. Clean kill.
It bears mentioning that this was with a 12 gauge flintlock.
Hope this info is useful.
Al
ps: Like Mooncoon, I follow much the same procedure when loading bp shotshells, too.
